In recent years, discorotron charging devices have been utilized for depositing charge on an adjacent surface, such as the photoreceptor of a xerographic reproduction system. Such discorotron charging devices employ a corona discharge electrode in the form of a wire coated with a relatively thick dielectric material and connected to an a.c. source of appropriate magnitude. The wire is surrounded on one side by a d.c. biased shield and on the other side by a grounded plane supporting the surface to be charged.
The electrical circuit equivalent of a discorotron charging device includes a resistor representing the corona discharge path, a capacitor, representing the dielectric material, in series with the resistor, and distributed capacitance in parallel with the series RC circuit. Due to the nature of the electrical equivalent, a low frequency square wave drive voltage applied to a dicorotron will be differentiated and therefore increased voltage will be required to achieve a desired square wave output waveform. At higher frequencies, the square wave drive voltage will produce a more square output waveform, but that waveform will contain undesirable current peaks at the voltage transitions. Another problem associated with a square wave drive voltage is that it does not permit power retrieval and hence is inefficient.
A more appropriate drive voltage for a dicorotron is a sine wave. Sine waves can be derived from resonant circuits which are efficient since they permit power retreival from reactive loads.
A classic approach to producing a sine wave power supply is to have complimentary emitter followers drive an LC network connected to the primary of an output transformer. However, the emitter follower approach is power dissipative since the emitter followers are operating in a low power dissipating mode only during the actual power input cycle. During the remainder of the power input cycle, the approximate sine wave function of the current through the inductor of the LC network must be conducted into the emitter followers. Since the emitter followers are connected conventionally to positive and negative dc supplies, the latter current conduction is transformed into heat losses. Thus, a non-dissipative sine wave power supply is desired for dicorotron charging and other devices since heat losses cannot be absorbed by the microelectronic components associated with desired high frequency operation.